It is estimated that 74,000,000 people in the United States have foot problems. The most common foot disorder in patients of all ages is pes planus, or flat foot which may be a painful, disabling condition. There is some debate regarding the optimum surgical treatment method because of shortcomings of standard arch reconstruction procedures. The main goal of the proposed investigation is to address problems associated with reconstructive operations of the arch of the foot. More specifically, two studies are planned to increase the basic understanding of foot mechanics by analyzing the kinematics and stability of the arch, and a third study is planned to apply results toward the development of arch reconstruction procedures. Study l : Three-dimensional kinematics and joint contact behavior of the normal arch of the foot will be studied in vitro using a magnetic tracking system under physiological loading conditions. Results will be used to test the hypothesis. H1: Physiologic loading of the arch results in significant displacement of all the joints constituting the arch and significant changes in joint contact characteristics. Study 2: Cadaveric foot specimens will be tested under different loading conditions with sequential sectioning of six structures stabilizing the arch to create arch instability (pes planus or flat foot deformity). Anatomic elements will be sectioned in different sequences and the relative contribution of each structure to stability determined. Two hypotheses (H2 and H3) will be tested. H2: Superficial deltoid and talocalcaneal ligaments are the most important static structures responsible to maintain arch stability. H3: Total joint contact area and contact distribution at talonavicular and subtalar joints are significantly altered in pes planus. Study 3: Using data from first and second studies, arch reconstruction operations will be developed and compared based on kinematics and stability. Two hypotheses will be tested (H4 and H5). H4: Standard operations such as flexor digitorum longus tendon transfer do not effectively restore alignment or stability of the arch or joint contact characteristics. H5: Deltoid ligament advancement significantly improves arch alignment and stability and joint contact characteristics.